/Engine/Source/Runtime/Experimental/Iris/Core/Public/Iris/ReplicationState/Private/IrisFastArraySerializerInternal.h
Mutable access to Item, will call MarkItemDirty
[FastArrayItemType](API\Runtime\IrisCore\Iris\ReplicationState\Private\TIrisFastArrayEditor\FastArrayItemTyp-) & operator[] ( int32 ItemIdx )